1. Technical Field
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method and package for a multi-die module which employs stacked dies.
2. Background Art
Semiconductors, or computer chips, have made their way into virtually every electrical product manufactured today. Chips are used not only in very sophisticated industrial and commercial electronic equipment, but also in many household and consumer items such as televisions, clothes washers and dryers, radios and telephones. As many of these types of products become smaller but more functional, there is a need to include more chips in these smaller products. The reduction in size of cellular telephones is one example of how more and more capabilities find their way into smaller and smaller electronic products.
The popularity of smaller and more complicated electronic products has placed increased demands on the packaging for chips used in such devices. These increased demands have led to new chip packaging concepts and approaches. Unpackaged chips are referred to as die or dies, and current packaging methods include placing more than one die in a single package. One such approach is to stack one die on top of another and then enclose the stack of dies in one package. The final package for the multiple-stacked semiconductor dies is much smaller than would result if the dies were each packaged separately. In addition to providing a smaller size, these packages offer a number of advantages that relate to the manufacturing of the package such as ease of handling and assembling.
An example of a die stacking technique incorporates a pair of stacked dies encapsulated in a molded plastic package that has connectors or leads extending out from the package which function as input/output terminals of the die inside the package. The package includes a substrate and a first die mounted on the top surface of the substrate. A second die is then stacked on top of the first die.
The substrate may be comprised of a flexible resin tape, a rigid fiber-glass/copper sheet laminate, a co-fired ceramic coupon, or a flexible metal lead frame, a ball grid array substrate or other well-known types of substrates in the semiconductor industry, depending on the particular type of semiconductor package being used.
The first die is conventionally mounted to the top surface of the substrate with, for example, a layer of an adhesive or an adhesive film, and then electrically connected to the substrate by a plurality of fine, conductive wires, typically gold (Au) or aluminum (Al), that electrically connects the die to the substrate. The wires are attached to the die at the bonding pads of the die which are located around the periphery of the die.
The second die is mounted on the top surface of the first die with an adhesive layer that is positioned within the central area of the top surface of the first die. The adhesive layer may contact or cover both the bonding pads of the first die and the conductive wires bonded to the first die. The adhesive layer positions the second die sufficiently far above the first die to prevent the dies from contacting each other or any wires connected to the dies. The second die is then wire bonded to the substrate in the same fashion as the first die. One or more additional dies can then be stacked on top of the second die using the same technique.
In a stacked die arrangement, the dies are wire bonded sequentially, typically with automated wire bonding equipment employing well-known thermal-compression or ultrasonic wire bonding techniques. During the wire bonding process, the head of a wire bonding apparatus applies a downward pressure on a conductive wire held in contact with a wire bonding pad on the die to weld or bond the wire to the bonding pad on the die.
After the dies are wire bonded to the substrate, the dies, substrate, and conductive wires are covered with plastic, or other suitable material, which encapsulates the stacked dies and protects them from moisture and other environmental elements.
Despite efforts to overcome problems resulting in lower yields of semiconductor packages with stacked dies problems still exist. In particular, dies within the stack fail prematurely.
Solutions to these problems have been long sought, but prior developments have not taught or suggested satisfactory solutions and, thus, solutions to these problems have long eluded those skilled in the art.
The present invention provides a semiconductor package with stacked dies and a method of manufacture therefor. A first die is attached to a substrate. A protective layer is placed on the first die over a central area thereof. The first die is electrically connected to the substrate. An intermediate adhesive layer is applied over the protective layer. A second die is attached to the intermediate adhesive layer and electrically connected to the substrate. This package and method increases the yield of semiconductor packages with stacked dies as well as device reliability.
Other advantages in addition to or in place of those mentioned above will become apparent to those skilled in the art from a reading of the following detailed description when taken with reference to the accompanying drawings.